Hydrogels are an important platform technology for biomedical applications in many areas, including managing chronic ailments, such as rheumatoid arthritis and osteoporosis, and treating acute conditions, such as hemorrhaging and cancer. Their utility is due in part to their high water content and tunable mechanical properties, which makes them inherently similar to living tissue. Hydrogels have been widely investigated for contact lenses, as materials for controlled drug release, and as scaffolds for load-bearing connective tissue.
The engineering or regeneration of load-bearing tissues is critically important for the repair of a broad range of defects with diverse causes, such as acute injuries or chronic tissue degradation. Artificial tissue matrices formed from polymeric materials are an essential component in the “toolbox” of tissue engineers, offering several important advantages over hard materials, such as ceramic and metallic implants, including: biodegradability, remoldability, injectability, and viscoelastic behavior programmable to match the response of the target tissue. Hydrogels are particularly promising biomaterials because their high water content, high porosity, modular synthesis, and ease of processing are suitable for a number of high value tasks, such as the encapsulation and injectable delivery of viable cells. Nevertheless, hydrogels often suffer from poor mechanical properties (e.g., low stiffness and toughness) that limit their application to the engineering of soft tissues, such as nerve tissue, or for use as substrates for the maintenance and study of laboratory cell strains in vitro. If used to regenerate connective tissues, these materials typically require mechanical isolation of the defect site, and are subject to degradation and clearance faster than replacement tissue can be formed. Hydrogels able to serve as robust, load-bearing materials, support the growth of encapsulated or invading cells, and ultimately lead to the regeneration of mature connective tissues (such as bone or cartilage) remain elusive. Thus, there is an unmet need for a simple hydrogel formulation capable of yielding tough biomaterials for the engineering of load-bearing tissues.